1. Field of the Invention
The present disclosure relates to image processing, and more particularly to image enhancement such as used in systems with multi-spectral sensors.
2. Description of Related Art
Remote sensing systems may acquire different spectral bands at different spatial resolutions. This is primarily due to a trade-off between the signal-to-noise ratio (SNR) and spatial/spectral resolution of the captured imagery. The SNR of the image depends on the amount of light (photons) captured by the sensor. The SNR can therefore be improved by opening up the spectral bandwidth to let in more light and/or increasing the size of the pixel, which reduces the spatial resolution. Consequently broad-band photographic imagery can afford to have smaller pixels and hence increased spatial resolution as compared to narrow-band hyper-spectral imagery. Optimal spatial sampling resolution is also dictated by the modulation transfer function (MTF) of the optics, which is wavelength dependent. Longer wavelength light has inherently reduced spatial resolution so long-wave bands can be sampled using larger pixels without any loss of information. The reduced spatial resolution at longer wavelengths serves both to improve the SNR as well as the transmission bandwidth of the collected imagery. For mixed modality imagery such as LIDAR, synthetic aperture radar (SAR), and hyper-spectral imagery (HSI), the optimal spatial resolution is dictated by the underlying physics and technology. Consequently imagery from different modalities will typically vary in the captured spatial resolution.
It is often desirable to increase the spatial resolution of low-resolution imagery to match the resolution of high resolution imagery both within and across remote sensing systems. Some methods involve using a higher resolution image to enhance a lower resolution image where both images were obtained at different bands by a multi-spectral sensor. Such methods only work when there is a spectral overlap between the high-resolution band and the low-resolution band. These techniques use information from the high resolution band, and the amount of sharpening applied to the low-resolution image cannot be controlled. Some solutions to these problems have been implemented, such as Gram-Schmitt spectral sharpening. However this still suffers to some extend from the limitations explained above.
Such conventional methods and systems have generally been considered satisfactory for their intended purpose. However, there is still a need in the art for improved image enhancement. The present disclosure provides a solution for this need.